Nearly every national military in the world has at least some kind of missile system. And a few have dozens of types of missiles. One common type is called an air-to-surface missile because it is fired from an aircraft and hits a target on either the ground or ocean. There are also surface-to-surface missiles, surface-to-air missiles, and air-to-air missiles. Whatever kind it may be, a modern missile is an extremely dangerous and effective weapon. For one thing, it travels alarmingly fast. That makes it a very difficult to shoot down. Also, missiles can and often do carry large amount of explosive materials. Some even carry nuclear warheads. It is no wonder that scientists are constantly looking for ways to counter missile technology, which revolutionized warfare in the past century.